1. Field of the Invention
The present invention relates to a heat treatment apparatus for heating a thin plate-like precision electronic substrate (hereinafter, simply referred to as “substrate”), such as a semiconductor wafer and a glass substrate for a liquid crystal display device, by irradiating the substrate with light.
2. Description of the Background Art
Conventionally, in a process for manufacturing a semiconductor device and the like, various types of heat treatments are performed on a substrate such as a semiconductor wafer. As a heat treatment method on the semiconductor wafer, a rapid thermal process (RTP) has been in wide use. In a typical RTP apparatus, a semiconductor wafer held in a chamber is irradiated with light emitted from halogen lamps, so that the temperature of the semiconductor wafer is raised to a predetermined processing temperature in a short time of about several seconds. Rapidly raising the temperature of the semiconductor wafer achieves activation of impurities implanted through, for example, an ion implantation process, with suppression of diffusion of the impurities. By using the RTP apparatus, a spike annealing is also performed in which the temperature of a semiconductor wafer is rapidly raised without being held at the processing temperature and then, when the semiconductor wafer reaches the processing temperature, simultaneously a rapid drop in the temperature of the semiconductor wafer is started.
In this RTP apparatus, as disclosed in Japanese Patent Application Laid-Open No. 2003-86528 for example, a plurality of halogen lamps are divided into a plurality of zones and a pyrometer (radiation thermometer) corresponding to each of the zones is provided, so that an output of the halogen lamps is controlled on a zone basis based on a wafer temperature measured by the pyrometer. The pyrometer can measure the temperature of only a partial region of the semiconductor wafer. Therefore, in the RTP apparatus, the semiconductor wafer is rotated during the heat treatment, and thereby an average temperature among concentric zones is calculated. Based on the calculated result, a feed-back control on the halogen lamps is performed.
However, in the conventional RTP apparatus, in order to rotate the semiconductor wafer, it is necessary to provide a rotation mechanism in the chamber. Providing a wafer rotation mechanism in the chamber complicates a configuration of the apparatus and increases the size of the chamber. In addition, a problem arises that particles are inevitably generated from the rotation mechanism and scattered within the chamber.
Moreover, in a case of measuring the temperature while rotating the semiconductor wafer relative to the pyrometer, the average temperature among the concentric zones is measured. Therefore, it is impossible to detect local non-uniformity in the temperature distribution. Accordingly, in a case where a temperature drop region (cold spot) locally appears, a measurement temperature of the entire concentric region including the cold spot is lowered. Performing the feed-back control on the output of the halogen lamps based on such a measurement result may cause concentric non-uniformity in the temperature distribution.
In recent years, a back side annealing is attracting attention, in which the semiconductor wafer is irradiated with light at a back surface thereof, on which there is no pattern dependency of the light absorption rate. In a case of performing the back side annealing in the RTP apparatus, it is necessary to ensure access to the back surface of the semiconductor wafer to be irradiated with light, and therefore, it is necessary to support a peripheral portion of the wafer. This makes it likely that a temperature abnormality occurs particularly in the peripheral portion of the semiconductor wafer, which may cause warping of the wafer.